Diesel Exhaust Soot Sensor System and Method

ABSTRACT

Systems and methods to determine when regeneration of a diesel particulate filter (DPF) are presented. Such determination is made by indirectly determining soot accumulation in the DPF by monitoring soot accumulation on a regeneration burner spark plug based on the correlation between spark plug fouling and DPF soot loading. An ion current sensing circuit is used during periods of no flame to determine soot loading on the spark plug. When soot loading on the spark plug approaches an amount that could cause fouling of the spark plug, the ignition controller initiates a hot spark to burn the soot off the spark plug. The number of such cleaning events is tracked and used to determine when the DPF soot loading is at a level that regeneration should be initiated. Temperature rise across the DPF is monitored and used to adjust the number spark plug cleaning events needed before initiating regeneration.

FIELD OF THE INVENTION

This invention generally relates to diesel particulate filter (DPF) systems and more specifically to a system and method for determining soot accumulation in a DPF to more effectively initiate a regeneration process to burn off the accumulated soot in the DPF.

BACKGROUND OF THE INVENTION

Increasing environmental restrictions and regulations are causing diesel engine manufacturers and packagers to develop technologies that improve and reduce the impact that operation of such engines have on the environment. As a result, much design work has gone into the controls that operate the combustion process within the engine itself in an attempt to increase fuel economy and reduce emissions such as NO_(x) and particulates. However, given the operating variables and parameters over which a diesel engine operates and given the tradeoff between NO_(x) and particulate generation, many engine manufacturers and packagers have found it useful or necessary to apply exhaust after-treatment devices to their systems. These devices are used to filter the exhaust gas flow from the diesel engine to remove or reduce to acceptable levels certain emissions. Such devices are particularly useful in removing exhaust particulates, or soot, from the exhaust gas flow before such soot is released into the environment.

One such exhaust after-treatment device is called a Diesel Particulate Filter (DPF). The DPF is positioned in the exhaust system such that all exhaust gases from the diesel engine flow through it. The DPF is configured so that the soot particles in the exhaust gas are deposited in the filter substrate of the DPF. In this way, the soot particulates are filtered out of the exhaust gas so that the engine or engine system can meet or exceed the environmental regulations that apply thereto.

While such devices provide a significant environmental benefit, as with any filter, problems may occur as the DPF continues to accumulate these particulates. After a period of time the DPF becomes sufficiently loaded with soot that the exhaust gases experience a significant pressure drop passing through the increasingly restrictive filter. As a result of operating with an overly restrictive filter, the engine thermal efficiency declines because the engine must work harder and harder simply to pump the exhaust gases through the loaded DPF. Besides the reduced thermal efficiency, a second and potentially more dangerous problem may occur. Because the soot accumulated in the DPF is flammable, continued operation with a loaded DPF raises the serious potential for uncontrolled exhaust fires if and when the accumulated soot is eventually ignited and burns uncontrollably.

To avoid either occurrence the engine packager typically incorporates one of several possible filter heating devices upstream of the DPF to periodically clean the filter. These filter heating devices are used periodically to artificially raise the temperature of the exhaust stream to a point at which the accumulated soot will self-ignite. When initiated at a time before loading of the DPF becomes excessive, the ignition and burn off will occur in a safe and controlled fashion. This process of burning the soot in such a controlled manner is called regeneration. The control of the method to generate the supplemental heat necessary to increase the temperature in the DPF is critical to the safe and reliable regeneration. Typically the acceptable regeneration range is from 600 to 900° C. Temperatures below this range are insufficient to ignite the accumulated soot, and temperatures above this range may cause thermal damage to the filter media.

Many methods have been devised to provide the auxiliary heat necessary to initiate regeneration. For example, the operating parameters of the diesel engine may be modified in such a manner to cause the exhaust temperature to rise to a level sufficient for proper operation of the downstream particulate filter. It is also possible to inject hydrocarbon fuel into the exhaust of a diesel engine immediately before the exhaust passes through a Diesel Oxidation Catalyst (DOC) positioned upstream of the particulate filter. The DOC converts the excess hydrocarbon fuel into heat by means of the catalytic reaction of the catalyst, thus increasing the exhaust gas temperature prior to its passage through the particulate filter. Supplemental heat may also be generated in the exhaust flow by use of an auxiliary electrical heater placed within the exhaust path. This supplemental heat is added to the exhaust gas prior to its passage through the particulate filter. As an alternative to the use of an electric heater, another method of filter regeneration uses a fuel-fired burner to heat the exhaust gas prior to the DPF. Such a burner requires a diesel fuel supply, an auxiliary air supply, and an ignition system.

The rate at which soot accumulates in the filter depends entirely upon the operating regime of the engine. As such, besides the selection of the particular method or device to be used to heat the exhaust gas to enable regeneration, the engine manufacturer or packager must also determine when to initiate the regeneration process. If regeneration is initiated too soon when the DPF is only lightly loaded, the process will be inefficient. If the regeneration is not initiated until the DPF is heavily loaded, the overall engine efficiency would have been unduly reduced as discussed above and there is a risk that the soot may self-ignite and/or that the burn may be unsafe and uncontrolled.

In an attempt to properly determine when to initiate the regeneration process, several sensors and control algorithms have been developed. These sensors and control algorithms are used to estimate the soot loading of the DPF so that regeneration can be initiated only after soot loading could cause an engine efficiency reduction but before excessive loading occurs actually resulting in such an efficiency reduction and raising the potential for self-ignition.

BRIEF SUMMARY OF THE INVENTION

In view of the above, embodiments of the present invention provide new and improved systems and methods for determining soot accumulation in a DPF to more effectively initiate a regeneration process to burn off the accumulated soot in the DPF in a safe and controlled manner, and to effectuate same.

A system and method in accordance with one embodiment of the present invention utilizes a fuel-fired heater and indirectly measures the soot accumulation in a DPF by monitoring soot accumulation on the burner spark plug. This is based on the discovery that and investigation of a strong correlation existing between spark plug fouling and DPF loading. More specifically, an ion current sensing circuit used to detect the presence of flame in the burner during the regeneration process is used during periods of no flame to determine soot loading on the spark plug. When soot loading on the spark plug approaches an amount that could cause fouling of the spark plug, the ignition controller initiates a hot spark to burn the soot off the spark plug. The number of such cleaning events is tracked and used to determine when the DPF soot loading is at a level that regeneration should be initiated.

In one embodiment, an adaptive algorithm is used to adjust the number of spark plug cleaning events that must be accomplished before regeneration of the DPF is initiated. Temperature rise across the DPF during the regeneration process is monitored. If the temperature rise is higher than a predetermined threshold, indicating that the soot accumulation is greater than expected before the regeneration process was initiated, then fewer spark plug cleaning events will be used to initiate regeneration. If the temperature rise is lower than a threshold, indicating that the soot accumulation is less than expected before the regeneration process was initiated, then more spark plug cleaning events will be allowed before initiating regeneration. In an embodiment, engine operating conditions, such as engine speed, may be used to preclude changes under certain conditions where temperature deviations are expected.

Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

FIG. 1 is a simplified system level diagram of DPF soot loading determination and regeneration system constructed in accordance with one embodiment of the present invention;

FIG. 2 is a simplified schematic block diagram illustrating an embodiment of a dual energy ignition and ion current sensing circuit constructed in accordance with the teachings of the present invention;

FIG. 3 is a flow diagram illustrating an aspect of a method performed in accordance with one embodiment of the present invention;

FIG. 4 is a flow diagram illustrating another aspect of a method performed in accordance with an embodiment of the present invention;

FIG. 5 is a simplified schematic block diagram illustrating an embodiment of a dual energy ignition and ion current sensing circuit constructed in accordance with the teachings of the present invention utilizing a surface gap spark plug;

FIG. 6 is a simplified system level diagram of DPF soot loading determination and regeneration system constructed in accordance with an alternate embodiment of the present invention;

FIG. 7 is a simplified system level diagram of DPF soot loading determination and regeneration system constructed in accordance with another embodiment of the present invention;

FIG. 8 is a graphical illustration of spark plug cleaning events versus time at a moderate soot loading rate;

FIG. 9 is a graphical illustration of spark plug cleaning events versus time at a low soot loading rate; and

FIG. 10 is a graphical illustration of spark plug cleaning events versus time at a minimal soot loading rate.

While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, there is illustrated in FIG. 1 an embodiment of a system 100 constructed in accordance with the teachings of the present invention that is capable of determining an appropriate time to initiate regeneration of a diesel particulate filter (DPF) 102. As discussed above, the DPF 102 is installed before or upstream of an exhaust outlet 104 to filter out particulates from the diesel engine exhaust. In order to clean the collected particulates, e.g. soot, off of the DPF 102, a burner 108 may be used upstream of the DPF 102 but downstream from the exhaust inlet 106 from the engine. Such a burner 108 may be any source of auxiliary heat, such as a fuel fired burner, and electrical burner, RF burner, DOC, or via modified engine operation. The engine exhaust gases flow through openings 114 of the burner 102 and through the DPF 102 before exiting into the environment via the exhaust outlet 104.

In a fuel fired burner 108 fuel and air are supplied via a fuel valve 110 and an air valve 112, e.g. such as electrically controlled solenoid valves. The fuel and air mixture is then ignited by one or more spark plugs 116, 118 positioned therein. In the illustrated embodiment, spark coils 120, 122 are driven by an ignition controller 124, such as the SmartFire® ignition system sold by the assignee of the instant application, to energize the spark plugs 116, 118. It should be recognized, however, that the high energy sparking and leakage current monitoring may be incorporated in a separate controller that may or may not include the ion sensing capabilities of the SmartFire® ignition system. As illustrated, the ignition controller 124 may be able to communicate with the engine management system (EMS) 126, and may receive various engine and system operating parameters, such as from an engine speed sensor 128, a throttle position sensor 130, a back pressure sensor 132, etc. The ignition controller 124 in one embodiment also receives exhaust temperature input from sensors 134, 136, 138 positioned to sense the temperature at different locations throughout the system 100.

As may be seen from the simplified illustration of FIG. 1, an advantage of this embodiment is that the system 100 does not require the addition of a separate sensor or sensors, but instead uses the existing one or more spark plugs 116, 118 in the burner 108 to detect the soot loading in the DPF 102. The spark plug's primary function is to ignite the flame in the burner 108 when the ignition controller 124 initiates the regeneration process. However, in the illustrated embodiment and as will be discussed more fully below with regard to FIG. 2, the spark plug(s) 116 and/or 118 is/are also used to detect the burner flame during regeneration by monitoring ion current flow across the spark plug's spark gap.

As may be seen in FIG. 2, a bias voltage (typically in the range of 100 to 500 volts) is applied from secondary power source 144 through electrical circuit 150 to the positive electrode of the spark plug 118 by the ignition controller 124. If no conductive path exists across the spark gap, then no current will flow in the electrical circuit 150. When the burner flame is present during regeneration, the flame ions and free electrons will provide a conductive path in the spark gap, and a small current (called ion current) will flow from the positive electrode to ground due to the applied bias voltage. The flame is easily detected by the ionization analysis circuitry 148, which monitors the magnitude and frequency of the ion current. All flames exhibit some oscillatory ion current due to the generally oscillatory nature of the flame.

Aside from ion currents produced by the flame, it has been determined that a second source of current flow may exist for the burner spark plug 118. To understand this, it is instructive to discuss the operating environment in which the spark plugs 116, 118 exist. During normal operation when the burner 108 is not producing a flame, the spark plugs 118 is continuously exposed to the passing exhaust gases. These unfiltered gases contain carbon particles which are largely removed after passing through the downstream DPF 102. It has been observed that spark plugs 118 mounted in the burner 108 gradually become coated with soot from the passing exhaust gases. A spark plug will typically exhibit an electrical resistance of 50,000 ohms or greater (essentially infinite) when completely clean. However, since this carbon soot deposited on the spark plug during normal operation is electrically conductive, the spark plug may exhibit an electrical resistance from around 20,000 ohms when lightly coated to as low as 1,000 ohms for a heavy coating, i.e. when the spark plugs 118 are excessively fouled.

In one embodiment of the present invention as shown in FIG. 5, the spark plug 118 used is of a surface gap design, such as, e.g., a design similar to that disclosed in U.S. Pat. No. 4,870,319, entitled Spark Plug with Creepage Spark Gap. As illustrated, the spark plug 118 includes a grounded shell 200 terminating at a first end 202. A center electrode 204 is positioned within the grounded shell 200 and extends axially beyond the first end 202 a first distance. A ceramic insulator 206 is positioned radially between the grounded shell 200 and the center electrode 204. The ceramic insulator 206 extends axially beyond the first end 202 of the grounded shell 200 a second distance which is less than the first distance so as to expose an end of the electrode 204. As may be seen from FIG. 5, the grounded shell does not include a projection extending beyond the first end 202 thereof. In this way the spark path is defined from the electrode 204, along an outer surface of the ceramic insulator 206, to the first end 202 of the grounded shell 200. In this embodiment, it is actually the ceramic insulator 206 that becomes coated with soot, thereby providing a lower resistance path to ground than a clean ceramic. Sparking actually burns the soot off the ceramic surface exposing the clean ceramic and eliminating the lower resistance path to ground.

In many conventional ignition systems if this soot coating is allowed to accumulate the spark plug will be unable to create an adequate spark to ignite the flame when the system controller calls for regeneration. However, the ignition system disclosed by VanDyne et al. in U.S. Pat. No. 5,777,216, the teachings and disclosure of which are incorporated herein in their entireties by reference thereto, has a unique dual energy circuit which creates a spark of sufficient heat to completely burn off the accumulated soot on the spark plug. Additionally, this dual energy ignition system has circuitry to monitor the ion current present during the combustion process, circuitry that can also be used to monitor the leakage current across the electrodes of the spark plug that is affected by the accumulated soot thereon. For ease of reference, this dual energy ion-sensing ignition system may be referred as a DEIS ignition system.

An embodiment of such a DEIS ignition system may be utilized as the ignition controller 124 illustrated in FIGS. 1 and 2. As shown in more detail in FIG. 2, the ignition controller 124 includes the primary power source 142 that is used to generate the energy from the battery 140 to create the spark in the spark gap when the triggering circuitry 146 is fired. The secondary power source 144 is used to create the ionization current in the spark gap, and the ionization analysis circuitry 148 is used to detect that ionization current.

With a firm understanding of the operating environment, soot accumulation effect, and operation of the DEIS ignition system in hand, operation of the system 100 may be better understood. Specifically, the following will now describe how embodiments of the present invention utilize the soot accumulation on the spark plug and the self-cleaning abilities of the DEIS ignition system to estimate the soot loading of the DPF 102 and properly initiate and control the regeneration process.

As discussed above, during normal operation the diesel engine continuously produces soot which passes over the spark plug 118 and is collected downstream in the DPF 102. In one engine operating scenario the DPF 102 may be able to operate to collect soot for one hour before the maximum soot loading is achieved (causing excessive back-pressure on the engine exhaust system). During that same period the spark plug 118 has also been accumulating soot.

FIG. 3 illustrates an embodiment of the process flow that is used in a method of the present invention. Once the method has begun at block 152, to detect the level of accumulated soot on the spark plug 118, the DEIS ignition system in the ignition controller 124, specifically the secondary power source 144, applies a bias voltage to the spark plug 118 when the burner flame is turned off. This may be done continuously, periodically, or intermittently in various embodiments. In the example just cited where the DPF 102 accumulates the maximum allowable soot loading in one hour, it was determined that the spark plug 118 would have accumulated enough soot in approximately two minutes to reduce its electrical resistance from essentially open circuit to 20,000 ohms. This amount of soot loading is still very mild and would not inhibit the creation of an adequate spark should the controller 124 attempt to initiate sparking for regeneration.

The ionization analysis circuitry 148 of the ignition controller 124 will detect the change in resistance across the spark gap of the spark plug 118 by monitoring the leakage current flow at block 154 in a manner similar to the monitoring of the ionization current during regeneration. When it is determined that a threshold value of soot loading has occurred, e.g. by determining if the leakage current is greater than a predetermined threshold leakage current flow due to contamination (Imax) at block 156, equating to a reduction in resistance to 20,000 ohms in this embodiment, the ignition controller 124 will initiate a high-energy spark for the sole purpose of cleaning the accumulated soot off of the spark plug 118 at block 158. After approximately two seconds of this high-energy spark, the ignition controller 124 ceases the commanded sparking. It then applies the bias voltage across the spark plug 118, and determines the electrical resistance. If the resistance indicates a clean spark plug, e.g. approximately 50,000 ohms or more, then no more sparking is necessary.

While this operation described so far is performed for the purpose of preventing the spark plug 118 from becoming fouled so that it will be able to ignite the fuel in the burner 108 when regeneration is required, it has been discovered that this operation may also be used to determine an optimal time for initiating the regeneration process itself. Such functionality eliminates the need for other sensors that are required to be used in prior systems to determine when filter soot loading has reached a point that requires regeneration.

The determination of the initiation time for regeneration is based on the discovered relationship between spark plug soot loading and soot loading of the DPF 102. As discussed above, in a typical DPF application with the engine operating at full power, the spark plug 118 will collect enough soot to require cleaning after approximately two minutes of operation. The appropriately sized DPF 102, however, can operate in the same environment for 60 minutes before reaching the maximum allowable soot loading. Therefore, in this case it may be deduced that after 30 cycles of spark plug cleaning the DPF 102 is fully loaded and in need of regeneration.

Indeed, as the level of soot production varies from moderate, to low, to minimal, the number of cleaning events per unit time decreases and the time between cleaning events increases as illustrated in FIGS. 8-10. While these figures illustrate that the time for the spark plug 118 to reach saturation varies with time even at the same soot production level, it can also be seen that there is a correlation between the frequencies of reaching the saturation point at the soot production level. However, it is clear that higher soot production levels such as illustrated in FIG. 8 decrease the time interval between saturation points, and that lower soot production levels such as illustrated in FIG. 9 and still lower in FIG. 10 increase the time interval between saturation points when a cleaning event is triggered.

As will now be apparent, in this embodiment the system will count the number of cleaning events by incrementing a count N at block 160 each time block 158 initiates a cleaning event. If decision block 162 determines that the number of cleaning cycles N now equals the predetermined threshold X, e.g. 30 for this example, then block 164 will initiate the regeneration process for the DPF 102 before ending at block 166. If the number of spark plug cleaning cycles is less than the predetermined threshold at block 162, then the method simply returns to monitoring the leakage current as discussed above.

Because diesel engines operate over a variable speed and load range, the soot loading in the DPF 102 is not consistent and cannot be estimated based purely on running hours. That is, the engine will emit differing amounts of soot per unit time depending on the actual operating conditions. However, regardless of engine operating conditions the spark plug 118 will accumulate soot, and therefore require cleaning, at a rate that is proportional to soot accumulation in the DPF 102 itself. As such, embodiments of the present invention need only count the number of cleaning cycles of the spark plug 118 to determine when regeneration should be initiated. This eliminates the sensors required in prior systems, along with the associated expense, complexity and reduction in reliability resulting from the use thereof.

In some installations this method of estimating DPF soot loading based on the number of cycles of spark plug cleaning may still not be completely accurate due to a variety of factors. One factor is the inconsistent deposition of soot on the spark plug 118 at some operating conditions and some burner 108 configurations. This may be due to slight changes in the flow field of the exhaust gas passing over the spark plug 118 at different engine operating conditions. Another factor may be the occasional erosion of the accumulated soot from the spark plug 118 due to debris impacting the spark plug 118 and chipping away some of the existing soot layer. Regardless of the source of variance of the relationship between spark plug soot loading and filter soot loading, in such installations an embodiment of the present invention that includes a method of adaptive tuning the operation and determination of the time to initiate regeneration may be used.

To fully understand the adaptive tuning strategy of this embodiment, the further discussion of the operation of the DPF regeneration is beneficial. The ignition controller 124 monitors three temperature sensors, to with, T1 134 upstream of the burner 108, T2 136 downstream of the burner 108 but upstream of the DPF 102, and T3 138 downstream of the DPF 102. When the ignition controller 124 determines that regeneration is required, the ignition controller 124 commands the fuel and air solenoid valves 110, 112 to open and commands the triggering circuitry 146 to trigger the spark plugs 116, 118 to begin sparking to create a flame in the burner 102.

The ignition controller 124 operates the burner 102, i.e. controls the fuel and air feed, such that T2 is within an acceptable range based on the installation and DPF 102 requirements, e.g. 400° C. to 600° C., to initiate regeneration. Once the accumulated soot in the DPF 102 begins to burn, T3 will increase above T2 because the incineration of the soot produces additional heat. T3 is monitored continuously during regeneration to make sure the DPF filter temperature is in the proper range for effective and safe regeneration.

If too much soot has been allowed to accumulate before regeneration is initiated, i.e. the rate of soot collecting in the DPF 102 is greater than the rate on which it is collecting on the spark plug 118, then the burning soot will create excessive heat, and T3-T2 will exceed the normal operating limits. If regeneration is initiated before sufficient soot has accumulated in the DPF 102, i.e. the rate of soot collecting in the DPF 102 is less than the rate on which it is collecting on the spark plug 118, then T3-T2 will be lower than the normal operating limits, which will not provide acceptable efficient operation. When either of these conditions is detected, an embodiment of the present invention adapts the control strategy for the initiation of the regeneration process as will be discussed more fully below with reference to FIG. 4.

As discussed above, the engine manufacturer or packager establishes the initial time for initiation of the regeneration process by setting the number of spark plug cleaning cycles “X” which must occur before regeneration is initiated. In the example discussed, X would initially be set at thirty. Once there have been X cleaning cycles, the regeneration process is initiated at block 168 as illustrated in FIG. 4. The ignition controller 124 measures the temperature rise across the DPF 102, i.e. T3-T2, as indicated at block 170. If decision block 172 determines that T3-T2 shows that the temperature rise across the DPF 102 is greater than the maximum temperature rise threshold “Y,” e.g. >700° C., meaning that too much soot has been allowed to accumulate, the number of cleaning cycles X is reduced by one as indicated at block 174 before the process ends at block 176. In other words, since the rate of soot accumulation on the DPF 102 must be greater than on the spark plug 118, regeneration should be initiated sooner (X−1 cleaning cycles) than initially thought. It will be recognized that the adjustment to the number of cleaning cycles at block 174 may be set at different values depending on the desired tuning response, and may vary the number based on the magnitude of temperature variation from the threshold.

If, however, the temperature rise is not greater than the maximum threshold Y at decision block 172, decision block 178 determines if the temperature rise is too low, i.e. below a predetermined minimum threshold “Z”, e.g. <300° C. This might indicate that regeneration was begun before it was needed because the rate of deposition of soot on the spark plug 118 was higher than on the DPF 102. If the temperature rise is too low, then decision block 180 is used to determine if the regeneration process is taking place during an idle condition, e.g. RPM<1000. If so, then the method loops back to the measure block 170. However, if the regeneration process is not occurring during an idle condition, then the required number of spark plug cleaning cycles X is incremented by one as indicated at block 182 to allow for more soot accumulation before initiating the regeneration process. It will be recognized that the adjustment to the number of cleaning cycles at block 182 may be set at different values depending on the desired tuning response, and may vary the number based on the magnitude of temperature variation from the threshold, similarly to that discussed above. If the temperature rise is within expected limits (a negative result from decision blocks 172 and 178), then the system simply continues to monitor the temperature rise during regeneration.

While certain advantages are realized by utilizing the spark plugs to detect the soot loading as discussed above, those skilled in the art will recognized from the foregoing description that the soot loading sensor electrodes may take on other forms as well, e.g. one or more spark plugs located within the exhaust flow path as disclosed by Kabasin in U.S. Pat. No. 5,253,475, one or more specialty electrodes in specific geometric arrangements as disclosed by Johnson et al. in U.S. Pat. No. 6,918,755 or Webb et al. in U.S. Pat. No. 7,032,376, one or more embedded electrodes as disclosed by Sakurai in U.S. Pat. No. 4,571,938 or Venghaus et al. in US Published Application No. 2006/0287802, or etc., the teachings and disclosure of each of these references are hereby incorporated in their entireties by reference thereto. As such, the use of the term “spark plug” herein and in the claims should be taken as an inclusive term including any structure that includes two electrodes with an insulator in-between on which soot can accumulate.

While the embodiment of the present invention illustrated in FIG. 1 utilizes the spark plug 118 to sense soot build up, this location is not limiting. Indeed, as illustrated in FIG. 6, a spark plug 600 located in the exhaust pipe prior to entering the burner 108 is used to perform the soot detection as described above.

In a further embodiment, illustrated in FIG. 7, a spark plug 700 is positioned after or downstream from the DPF 102 to monitor soot escaping from the DPF 102. In this position, which could be used with any of the foregoing embodiments, the spark plug 700 provides an additional diagnostic function to monitor the effectiveness of the DPF 102. If significant soot accumulates on the spark plug 700 in this location, it might indicate a crack forming in the DPF 102 which is allowing soot to escape. This spark plug 700 will detect the accumulated soot in the same manner described above and will similarly be cleaned. Each of these cleaning events will also be counted as described above. The determination of a problem or lack of efficiency of the DPF 102 may be made if the number of cleaning events exceeds a predetermined threshold or if a cleaning event is required within a predetermined period of time.

All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 

1. A method of regenerating a diesel particulate filter (DPF) with a fuel fired heater having a spark plug to initiate flame in a burner thereof, comprising the steps of: counting a number of cleaning events of the spark plug; and initiating regeneration when the number of cleaning events of the spark plug is greater than or equal to a predetermined threshold.
 2. The method of claim 1, further comprising the steps of: providing a bias voltage to the spark plug; monitoring a leakage current across a spark gap of the spark plug; and initiating the cleaning event when the step of monitoring determines that the leakage current exceeds a predetermined current threshold.
 3. The method of claim 1, further comprising the steps of: determining a value of resistance across a spark gap of the spark plug; and initiating the cleaning event when the step of determining indicates that the resistance is less than a predetermined resistance.
 4. The method of claim 1, further comprising the steps of: monitoring a temperature rise across the DPF during the regeneration; and reducing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF exceeds a predetermined maximum temperature threshold.
 5. The method of claim 1, further comprising the steps of: monitoring a temperature rise across the DPF during the regeneration; and increasing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF is less than a predetermined minimum temperature threshold.
 6. The method of claim 1, further comprising the steps of: monitoring a temperature rise across the DPF during the regeneration; determining an operating condition of a diesel engine from which exhaust flows to the DPF; and increasing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF is less than a predetermined minimum temperature threshold and when the step of determining determines that the diesel engine is not idling.
 7. The method of claim 1, further comprising the steps of: monitoring a temperature rise across the DPF during the regeneration; reducing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF exceeds a predetermined maximum temperature threshold; and increasing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF is less than a predetermined minimum temperature threshold.
 8. The method of claim 7, further comprising the step of determining an operating condition of a diesel engine from which exhaust flows to the DPF, and wherein the step of increasing is performed only when the step of determining determines that the diesel engine is not idling.
 9. A regeneration system for a diesel particulate filter (DPF) positioned to capture particulates in an exhaust flow from a diesel engine, comprising: a burner configured to be positioned upstream of the DPF in the exhaust flow, the burner including at least one spark plug positioned in the exhaust flow therethrough to ignite a flame therein during regeneration; an ignition controller operably coupled to the at least one spark plug to control sparking thereof during regeneration, the ignition controller including means for determining a level of soot accumulation on the spark plug, the ignition controller being configured to initiate a cleaning event of the spark plug when the level of soot accumulation exceeds a predetermined threshold; and wherein the ignition controller counts each cleaning event of the spark plug and initiates regeneration when the number of cleaning events exceeds a predetermined number.
 10. The regeneration system of claim 9, wherein the means for determining a level of soot accumulation on the spark plug comprises a power source configured to provide a bias voltage to a positive terminal of the spark plug at least when no regeneration is commanded and a current sense circuit for monitoring a leakage current flowing across a spark gap of the spark plug, and wherein the ignition controller initiates the cleaning event when the leakage current exceeds a predetermined maximum current threshold.
 11. The regeneration system of claim 9, further comprising a plurality of temperature sensors positioned to monitor a temperature rise across the DPF during regeneration, and wherein the ignition controller monitors the temperature rise across the DPF during regeneration and changes the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise is outside of expected values.
 12. The regeneration system of claim 11, wherein the ignition controller decreases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is greater than a predetermined maximum temperature threshold.
 13. The regeneration system of claim 11, wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold.
 14. The regeneration system of claim 11, further comprising an engine speed sensor operatively coupled to the ignition controller, and wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold and the engine speed sensor indicates that the engine is not idling during the regeneration.
 15. A diesel particulate filter (DPF) system for removing particulates from diesel engine exhaust, comprising: a diesel particulate filter (DPF) having an inlet and an outlet; a burner having an exhaust inlet for receiving diesel engine exhaust and a burner outlet coupled to the inlet of the DPF, the burner including a spark plug exposed to an exhaust flow through the burner; an ignition controller having a primary power source operably coupled through triggering circuitry to the spark plug to control sparking thereof, the ignition controller further including a secondary power source configured to provide a bias voltage to a positive electrode of the spark plug and an ion current sensing circuit operatively coupled between the secondary power source and the spark plug; wherein the ignition controller is configured to initiate a cleaning event when the ion current sensing circuit senses a current flow greater than a predetermined maximum leakage current threshold when not commanding regeneration of the DPF; and wherein the ignition controller counts each cleaning event of the spark plug and initiates regeneration of the DPF by turning on the burner when the number of cleaning events exceeds a predetermined number.
 16. The DPF system of claim 15, further comprising a plurality of temperature sensors positioned to monitor a temperature rise across the DPF during regeneration, and wherein the ignition controller monitors the temperature rise across the DPF during regeneration and changes the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise is outside of expected values.
 17. The DPF system of claim 16, wherein the ignition controller decreases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is greater than a predetermined maximum temperature threshold.
 18. The DPF system of claim 16, wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold.
 19. The DPF system of claim 16, further comprising an engine speed sensor operatively coupled to the ignition controller, and wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold and the engine speed sensor indicates that the engine is not idling during the regeneration.
 20. The DPF system of claim 15, wherein the ignition controller initiates a cleaning event by gating the triggering circuitry to generate a hot spark at the spark plug to burn off accumulated soot.
 21. A method of measuring soot flowing in an exhaust pipe having a spark plug positioned therein such that it accumulates soot thereon, the accumulated soot creating a path for electrical leakage current from a center electrode to a ground plane on a shell of the spark plug, the method comprising the steps of: providing a bias voltage to the spark plug; monitoring the leakage current; initiating a sparking event to clean the soot from the spark plug when the step of monitoring determines that the leakage current exceeds a predetermined current threshold; and counting a number of sparking events to clean the soot from the spark plug, the number of sparking events being indicative of an amount of soot flowing in the exhaust pipe.
 22. The method of claim 21, further comprising the step of initiating regeneration of a diesel particulate filter (DPF) positioned to filter soot flowing in the exhaust pipe when the number of cleaning events reaches a predetermined threshold.
 23. The method of claim 22, wherein the step of initiating regeneration comprises the step of turning on a fuel fired heater to initiate flame in a burner thereof to regenerate the DPF.
 24. The method of claim 22, wherein the step of initiating regeneration comprises the step of injecting hydrocarbon fuel into the exhaust pipe to cause a catalytic reaction in a Diesel Oxidation Catalyst positioned upstream of the DPF to regenerate the DPF.
 25. The method of claim 22, wherein the step of initiating regeneration comprises the step of modifying operating parameters of a diesel engine in such a manner to cause an exhaust temperature to rise to a level sufficient to regenerate the DPF.
 26. The method of claim 21, further comprising the steps of: positioning the spark plug downstream of a diesel particulate filter (DPF) positioned to filter soot flowing in the exhaust pipe; and providing an indication of a lack of effectiveness of the DPF and possible existence of a crack in a filter substrate when the number of sparking events exceeds a predetermined threshold. 